Fuses and anti-fuses are programmable electronic devices that are used in a variety of circuit applications. A fuse is normally closed or has a relatively lower resistance to allow electric current flowing therethrough, and when blown or programmed, it becomes open or has an increased resistance. An anti-fuse, on the other hand, is normally open or has relatively high resistance, and when an anti-fuse is blown or programmed, this results in a short circuit or a decreased resistance.
There are many applications for fuses and anti-fuses. One particular application is for customizing integrated circuits (IC's) after production. One IC configuration may be used for multiple applications by programming the fuses and/or anti-fuses (e.g., by blowing or rupturing selected fuses and anti-fuses) to deactivate and select circuit paths. Thus, a single integrated circuit design may be economically manufactured and adapted for a variety of custom uses. Fuses and anti-fuses may also be used to program chip identification (ID) after an integrated circuit is produced. A series of ones and zeros can be programmed in to identify the IC so that a user will know its programming and device characteristics. Further, fuses and anti-fuses can be used in memory devices to improve yields. Specifically, fuses or anti-fuses may be programmed to alter, disconnect or bypass active cells or circuits and allow redundant memory cells to be used in place of cells that are no longer functional. Similarly, information may be rerouted using fuses and/or anti-fuses.
One type of fuse device is “programmed” or “blown” by using a laser to open a link after the semiconductor device is processed. This type of fuse device not only requires an extra processing step to program or “blow” the fuse devices where desired, but also requires precise alignment of the laser on the fuse device to avoid destroying neighboring devices.
Another type of fuse device is electrically programmable, which is usually referred to as an “e-fuse” or an “e-anti-fuse,” by using a programming current or voltage that is higher than the circuit's normal operating current or voltage.
A conventional design for an e-fuse device includes a bottom polysilicon layer and a top metal silicide layer, which are patterned into two relatively wider contact regions that are electrically coupled together by a relatively narrower fuse region. Because metal silicide has a significantly lower sheet resistance than polysilicon, electrical current typically flows through the top metal silicide layer at an un-programmed state. Therefore, the resistance of the metal silicide layer determines the resistance of the e-fuse at such an un-programmed state. However, when a sufficiently large programming current is passed through the e-fuse, joule heating accumulated in the relatively narrower fuse region heats the metal silicide layer in the fuse region to a sufficiently high temperature, causing local agglomeration of the metal silicide layer in the fuse region and forming a discontinuity between the contact regions. The electric current is consequentially forced to flow through the underlying polysilicon layer instead, and the resistance of the e-fuse therefore increases significantly, due to the relatively higher sheet resistance of the polysilicon material. The increased resistance can be readily detected as indicative of a programmed state of the e-fuse.
However, programming of conventional e-fuses as described hereinabove requires relatively high power (e.g., ≧10 mW per fuse) and high temperatures (e.g., ≧1000° C.), which increase the size the fuse and significantly limit the usability of such e-fuses in integrated circuit (IC) chips.
There is therefore a need for improved electrical fuses that can be programmed at lower temperatures with less power consumptions. There is also a need for improved electrical fuses that can be readily integrated into IC chips, especially for use in conjunction with complementary metal-oxide-semiconductor (CMOS) circuits. There is further a need for electrical fuse designs that can be fabricated using standard CMOS process with no or few additional processing steps.